HTTP 500 after saving settings - clean install - debian 9

Hi,

I have installed Akaunting on my own clean debian 9 server, using the following guide:

The installation goes smoothly, but after I get through the installation pages and go to the settings page, I change the invoice prefix (by one letter) and hit save. Now the page becomes blank and a 500 internal server error is returned. This happends on all pages, so I'm unable to access the web interface anymore.

Each time I try to access the webpage, the following is written to the error log:

2019/03/06 12:05:17 [error] 22500#22500: *77 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Uncaught ReflectionException: Class config does not exist in /var/www/akaunting/vendor/laravel/framework/src/Illuminate/Container/Container.php:729
Stack trace:
#0 /var/www/akaunting/vendor/laravel/framework/src/Illuminate/Container/Container.php(729): ReflectionClass->__construct('config')
#1 /var/www/akaunting/vendor/laravel/framework/src/Illuminate/Container/Container.php(608): Illuminate\Container\Container->build('config')
#2 /var/www/akaunting/vendor/laravel/framework/src/Illuminate/Container/Container.php(575): Illuminate\Container\Container->resolve('config')
#3 /var/www/akaunting/vendor/laravel/framework/src/Illuminate/Foundation/Application.php(728): Illuminate\Container\Container->make('config')
#4 /var/www/akaunting/vendor/laravel/framework/src/Illuminate/Foundation/helpers.php(106): Illuminate\Foundation\Application->make('config')
#5 /var/www/akaunting/vendor/laravel/framework/src/Illuminate/Foundation/helpers.php(269): app('config')
#6 /var/www/akaunting/vendo" while reading response header from upstream, client: cencored-my-ip, server: cencored.my.domain.com, request: "GET / HTTP/1.1", upstream: "fastcgi://unix:/run/php/php7.0-fpm.sock:", host: "censored.my.domain.com"

Could you please let me know what could possibly be going wrong?
I can resolve this by deleting the akaunting files, redoanloading them and rebuilding the database, but then the error happends again once I try to save the settings change again.

Sorry, forgot to include the link, the guide used to install:
https://www.vultr.com/docs/installing-akaunting-on-debian-9

Update:
Above problem happens in version 1.3.12-Stable but not in 1.2.12-Stable